(a) Technical Field
The present invention relates to an interfacial polymer for a network used as a coupling agent in mixing of rubber-silica. More particularly, the present invention relates to an interfacial polymer for a rubber-silica network, that is, a block copolymer containing a copolymer of conjugated diene and vinyl aromatic monomers, in which when used as a coupling agent in the mixing of synthetic rubber and silica (an inorganic material), the polymer enhances silica dispersibility within the rubber, and improves compatibility and processability, resulting in considerable improvement in the dynamic property as well as the mechanical property of the rubber, and when used in a tire, etc., it enhances automobile braking performance and reduces rolling resistance.
(b) Background Art
In the case of styrene-butadiene rubber prepared by a solution polymerization method frequently used in the tire industry, it is possible to freely adjust the vinyl structure of butadiene, the styrene content, and the styrene molecular block rate according to tire requirements such as rolling resistance and wet traction. Thus, the styrene-butadiene rubber is frequently used in a tire tread. Also, in the styrene-butadiene rubber prepared by the solution polymerization method, it is easy to introduce several functional groups into a molecular end using organolithium catalyst.
Such introduction of functional groups into rubber increases the compatibility with an inorganic filler reinforcing material, that is, carbon black or silica. This improves the tread wear resistance of a tire, and thus improves durability of the tire. Further, it is possible to reduce rolling resistance, thereby improving the fuel efficiency of an automobile, and to improve the wet traction characteristic, thereby shortening an automobile braking distance.
In general, it is known that a silica reinforcing material is excellent in rolling resistance and wet traction characteristics as compared to carbon black. However, In the case of general rubber containing a vinyl monomer aromatic monomer and a conjugated diene copolymer, when the rubber is mixed with silica, its compatibility is known to be reduced. This is because unlike carbon black, hydrophilic silica is not sufficiently mixed with hydrophobic rubber, and thus the silica is not uniformly dispersed within the rubber.
In general, in order to solve such incompatibility between rubber-silica, a silane coupling agent having an alkoxy group is mainly used. Representatively, bis(triethoxysilylpropyl)tetrasulfide, called “Si69” (Degussa) is used. When such a silane coupling agent is used, an alkoxysilyl group reacts with a hydroxyl group on silica surface, resulting in a silane coupling reaction, and sulfur is cross-linked with rubber, thereby improving compatibility. This allows the rubber and the silica to be mixed.
A tire (hereinafter, referred to as silica tire) that uses the rubber mixed with the silica, as described above, seems to be excellent in wet traction and rolling resistance characteristics as compared to carbon black tire. Also, such characteristics of the tire are known to be improved in proportion to dispersion of silica within the rubber.
However, such a silane coupling agent is expensive, and also causes a volatile material during mixing. Further, it has a limitation in finely dispersing silica within rubber. Thus, the agent itself has a difficulty in showing physical properties of a high performance silica tire.
Due to carbon dioxide emissions control and automobile fuel consumption control, following global warming, the development of a silica tire of low fuel consumption and high performance has been recently more spotlighted. For this, in order to further improve compatibility of rubber-silica, besides the above described method of using a coupling agent such as Si69, there have been reported methods of more uniformly dispersing silica by introducing a functional group capable of giving hydrophilicity, into rubber.
U.S. Pat. Nos. 6,906,152 and 6,967,739 disclose the mixing of conjugated diene-based rubber modified with a multivalent glycidyl amino group, with silica, which can improve wet traction and rolling resistance properties.
Also, U.S. Pat. No. 7,241,842 discloses a technology of introducing a polyorganosiloxne functional group in synthesis of conjugated diene-based rubber, thereby reducing heat build up during mixing with silica, and improving wet traction and tread wear characteristics.
Also, U.S. Pat. Nos. 7,342,070 and 7,528,199 disclose a technology of using modified rubber which is added with an amino functional group including an alkoxysilyl group in a styrene-butadiene copolymer reaction, in which when a mixture of such modified rubber and silica is applied to a tire tread, physical properties of a tire can be improved due to low hysteresis.
Also, U.S. Pat. No. 6,841,648 discloses a technology of introducing a silyl ether functional group containing a carbamic acid chloride-based functional group and an epoxy group, into a styrene-butadiene copolymer, thereby improving wet traction and rolling resistance characteristics.
Also, U.S. Pat. No. 7,485,684 discloses a technology of introducing a nitrone functional group into the end of a styrene-butadiene copolymer, thereby improving a rolling resistance characteristic.
However, even In the case of the conjugated diene polymer introduced with a functional group, disclosed in the above patents, only when a silane coupling agent, such as expensive Si69, is applied in a large amount during mixing with silica, physical property improvement is expected. Also, in many cases where a functional group is introduced into a conjugated diene polymer, the functional group is introduced into both ends of the polymer or the middle of the polymer chain through a coupling reaction. In such cases, since it is difficult to introduce sufficient functional groups, there is a limitation in improving the compatibility with silica. Further, introducing functional groups can cause side-reactions, thereby making it difficult to perform the control of Mooney viscosity in a commercialization process, and the operation during purification process.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.